Manufacturing Technologies for Turbine Power Blades - Hybrid Anisotropic Materials for Wind Power Turbine Blades - page 115

4.9.10.1 Limitations

Rotationally. molded. parts. have. to. follow. some. restrictions. that. are. different.
from.other.plastic.processes..As.it.is.a.low-pressure.process,.sometimes.design-
ers.face.hard.to.reach.areas.in.the.mold..Good.quality.powder.may.help.over-
come.some.situations,.but.usually.the.designers.have.to.keep.in.mind.that.it.is.
not.possible.to.make.some.sharp.threads.used.in.injection.molded.goods..Some.
products. based. on. polyethylene. can. be. put. in. the. mold. before. illing. it. with.
the.main.material..This.can.help.to.avoid.holes.that.otherwise.would.appear.
in.some.areas..This.could.also.be.achieved.using.molds.with.movable.sections.
Another. limitation. lies. in. the. molds. themselves.. Unlike. other. processes.
where. only. the. product. needs. to. be. cooled. before. being. removed,. with.
rotational. molding,. the. entire. mold. must. be. cooled.. While. water. cooling.
processes. are. possible,. there. is. still. a. signiicant. down. time. of. the. mold..
Additionally,. this. increases. both. inancial. and. environmental. costs.. Some.
plastics.will.degrade.with.the.long.heating.cycles.or.in.the.process.of.turning.
them.into.a.powder.to.be.melted.

4.9.11 Conclusions

. 1.. Due.to.high.temperatures.within.the.mold,.the.plastic.must.have.a.

high. resistance. to. permanent. change. in. properties. caused. by. heat.
(high.thermal.stability).

. 2.. The. melted. plastic. will. come. into. contact. with. the. oxygen. inside.

the.mold;.this.can.potentially.lead.to.oxidation.of.the.melted.plastic.
and.deterioration.of.the.material's.properties..Therefore,.the.chosen.
plastic. must. have. a. suficient. amount. of. antioxidant. molecules. to.
prevent.such.degradation.in.its.liquid.state.

. 3.. Because.there.is.no.pressure.to.push.the.plastic.into.the.mold,.the.cho-

sen.plastic.must.be.able.to.low.easily.through.the.cavities.of.the.mold.

. 4.. The.part's.design.must.also.take.into.account.the.low.characteristics.

of.the.particular.plastic.chosen..Rotational.molding.process.for.cre-
ating.many.kinds.of.mostly.hollow.items,.typically.of.plastic,.can.be.
used.for.molding.web.spars.wind.turbine.blades.

References
.

1.. Brondsted,.P.,.H..Lilholt,.and.A..Lystrup..2005.. Composite material for wind power
turbine blades .. Roskilde,. Denmark:. Annual. Reviews,. A. Nonproit. Scientiic.
Publisher.. email:. [e-mail],. [e-mail],. aage.

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